1. Field of the Invention
The present invention relates to portable transmitters, in particular, equipped for use in a keyless-entry system capable of locking and unlocking various types of doors, for example, car doors without using any mechanical key.
2. Description of the Related Art
For example, there is a conventional portable transmitter for use in a keyless-entry system capable of locking and unlocking car doors without using any mechanical key. The conventional portable transmitter is comprised of an inner case, a circuit substrate, and an outer case. The inner case is comprised of a first case and a second case. The first case and the second case are assembled in one body. One or more push buttons are extended from the first case toward the outside of the first case, in other words, exposed externally. One or more tact switches are arranged on the circuit board at the position which is opposite to the push buttons. The circuit substrate is placed in the inner case. The outer case has opening parts through which the push buttons are exposed to the outside. The outer case accommodates the inner case so that the push buttons project through the corresponding opening parts of the outer case. For example, Japanese patent laid open publication number JP 2001-200664 discloses such a type of the conventional portable transmitter.
FIG. 8 is a view showing a cross section of a conventional portable transmitter having the above structure.
As shown in FIG. 8, the portable transmitter is comprised of an inner case J30 and an outer case J40. The inner case J30 is comprised of a first case J31 and a second case J32. The inner case J30 accommodates a circuit substrate J20 on which one or more tact switches J21 are mounted. The outer case J40 accommodates the inner case J30.
Specifically, the portable transmitter shown in FIG. 8, the first case J31 and the second case J32 are assembled in one body. The first case J31 has a bottom surface and side walls. The side walls enclose the bottom surface of the inner case J31. Similar to the first case J31, the second case J32 has a bottom surface and side walls. The side walls enclose the bottom surface of the inner case J32.
Further, one or more penetration holes (or through holes) J33 are formed in the first case J31 at the position which is opposite to the position of the tact switches J21 mounted on the circuit substrate J20. That is, the number of the penetration holes J33 is equal to the number of the tact switches J21 mounted on the circuit substrate J20.
Further, the inner case J30 accommodates a cover J10 so that a flange J11 of the cover J10 is sandwiched between the first case J31 and the second case J32. That is, the cover J10 has a bottom surface, side walls, and the flange J11. The side walls enclose the end part of the bottom surface of the cover J10. The flange J11 of the cover J10 is formed at the distal end part of the side walls.
The structure of the cover J10 prevents foreign matter such as dust, water and fine solid particles from entering into the inside of the portable transmitter through the penetration holes J33 and the matching faces between the first case J31 and the second case J32. That is, the structure of the cover J10 prevents the circuit substrate J20, etc. from being exposed to foreign matter such as dust, water and fine solid particles.
The outer case J40 has one or more opening parts J43 at the position which is opposite to the corresponding tact switches J21. That is, the number of the opening parts J43 corresponds to the number of the tact switches J21. Each of outer knobs J60 has a push button J63. The push button J63 of the outer knob J60 projects toward the inner case J30 side. The outer knob J60 is pushed onto the outer case J40.
In more detail, the outer knob J60 is placed in the corresponding opening part J43. A sheet J70 is placed between the outer knobs J60 and the first case J31. The sheet J70 is made of elastic material such as rubber. The sheet J70 has projection parts J71 which projects toward the outer knobs J60. The projection parts J71 of the sheet J70 correspond to the outer knobs J60 and the tact switches J21.
The front end part of each of the projection parts J71 in the sheet J70 is contacted with the corresponding push button J63. The part of the sheet J70 which is opposite to the front end part of the projection parts J71 is contacted with the cover J10. In the portable transmitter shown in FIG. 8, the projection parts J71 in the sheet J70 are elastically deformed and placed between the outer knobs J60 and the first case J31.
That is, as shown in FIG. 8, the outer knob J60 is placed in the corresponding opening part J43 while the outer peripheral edge part of the outer knob J60 is pushed toward the outer case J40 by repulsive elastic stress of the corresponding projection part J71.
When the user (or the driver) of a vehicle pushes one of the outer knobs J60 in the conventional portable transmitter having the above structure, the pushed force is applied to the corresponding contact switch J21 through the projection part J71 and the cover J10, the corresponding tact switch J21 is thereby turned on. When the tact switch J21 is turned on, one or more circuit modules formed on the circuit substrate J21 starts to execute a predetermined process according to the condition of the tact switch J21.
By the way, in the conventional portable transmitter having the above structure shown in FIG. 8, the outer knobs J60 and the outer case J40 are different members, respectively, not assembled into one body. That is, the outer peripheral edge part of the outer knob J60 is forcedly pushed onto the outer case J70 by repulsive elastic stress applied from the projection part J71 formed in the sheet J70. The recent trend in the technical field of the portable transmitters is to decrease the total number of components of the portable transmitter and the manufacturing cost thereof. The conventional portable transmitters do not satisfy the above trend.